1. Technical Field
This disclosure relates to novel substrates for the growth of materials by gas phase deposition technologies. More specifically, this disclosure relates to a substrate for growth of materials by gas phase deposition, the substrate having a temperature monitoring zone provided thereon and the use of non-contact optical pyrometry to measure the temperature of the substrate during growth of the material on the substrate. The materials and methods disclosed herein are particularly useful in monitoring the temperature of a substrate during the growth of semiconductors by gas phase deposition.
2. Background of Related Art
The growth of high quality semiconductors by gas phase deposition technology including chemical beam epitaxy (CBE) and metal organic chemical vapor deposition (MOCVD) depends strongly on the growth temperature. Therefore, active control of the substrate temperature throughout the growth process is very important for gas phase growth methods.
One method for substrate temperature monitoring is to use a thermocouple positioned at the backside of the substrate holder. However, this method does not provide the actual substrate surface temperature which may change during the growth process because of a change in the overall thermal radiation loss.
Non-contact optical pyrometry is sometimes used to determine the surface temperature of the substrate. The pyrometer is positioned to view a portion of the substrate and temperature readings are obtained throughout the growth process. Since the pyrometer views areas of the substrate where growth is occurring, a major disadvantage of this method is the presence of an interference effect produced during growth, particularly when the growth involves heterostructures. For example, during growth of an epitaxial layer having an optical constant which is different from that of the substrate material, the infrared radiation emitting through the epitaxial layer will undergo an apparent oscillation (ref) if the epilayer thickness is comparable to the optical wavelength at which the pyrometer functions. Unfortunately, the optical sensor of many pyrometers designed for such an application often operates at a wavelength of about 1 .mu.m which is comparable to a typical epilayer thickness. Thus, due to interference effects the pyrometer readout will shown an oscillatory behavior with respect to growth time even though a constant temperature is measured by a thermocouple positioned at the back side of the wafer. If the pyrometer readout is used for feedback control to maintain a constant optical temperature, some variation in true temperature is expected, especially when the epilayer thickness is comparable to the operating wavelength of the pyrometer. These temperature variations produce an undesirable variation in the quality and properties of the resulting semiconductors.
It would be desirable to be able to accurately monitor the temperature of the substrate during gas phase deposition of materials such as, for example, during semiconductor growth.